"The meat for-sex hypothesis is a plausible explanation for male-female meat sharing in this species," the pair wrote. "As chimpanzees are highly promiscuous, they have a certain degree of female choice and hunters can usually control the sharing of their catch.”

They came to their conclusions after studying chimps living in the Tai National Park in Ivory Coast for 22 months. The group comprised 49 individuals, including 5 adult males and 14 adult females and the data was collected between 2003 and 2006.

The team also found that males showed a tendency to share meat with females who were in their fertile period. However, they also shared meat with certain females outside of this fertile period, revealing a tendency of "exchanging services on a long-term basis".

The paper explains: "Females copulated more with males who shared meat with them than with males who did not share meat with them, irrespective of the rank of the male, the rank or age of the female, the association patterns of the dyad (group), the level of gregariousness of the female and the begging tendencies of each female towards each male."

There is a practical evolutionary benefit for both sexes, Gomes and Boesch said, as the exchange of meat "led to males increasing their mating success and females increasing their caloric intake without suffering the energetic costs and potential risk of injury related to hunting."

The team is now to carry out further studies on chimpanzee communities, "which take into account the degree of female choice in the group and the capacity of hunters to control the sharing of their catch." They hope that this will shed more light on the theory that early humans in hunter-gatherer societies may also have exchanged food for sex, and that accomplished hunters therefore had "increased reproductive success".